Coated container



Patented June 17, 1941 UM'IED COATED CONTAINER Victor Nelson and Alexander C. Herro, Oconomowoc, Wis., assignors to Carnation Company, Oconomowoc, Wis., a corporation of Delaware N Drawing.

Application February 8, 1939,

Serial No. 256,099 4 Claims.- (01. 220-64) ment of metallic surfaces whereby they are given f a highly resistant coating.

The present invention yet more particularly contemplates the treatment of tin and tin-containing materials in such a manner as to render the surfaces thereof stable and to confer thereon an increased resistance to known deterioration in character and appearance during use.

More particularly, while tin and tin-containing materials possess a relatively good resistance to corrosive influences and are, accordingly,-employed as a coating for the protection of less resistant metals, for example, nevertheless this coating and/or materials comprising tin are in general short of perfection in this regard in that deterioration may and frequently does occur, particularly in regard to the appearance of the tin surfaces under certain influences. Thus, for example, containers made of tin-plate are frequently attacked by many substances placed therein in more or less degree, the attack oftentimes causing the surfaces of the plated material to darken in color or to etch or to corrode, and in some cases attacking the plated coating sufficiently to expose some of the underlying base metal. Of the substances which cause, induce or i enhance the deterioration of the plated coating many food products form one example. For instance, milk and milk products have been known to cause the aforementioned blackening, corrosive efl'ects.

It is an object of the present process to obviate the above diificulties by providing tin or tin- .contain'ing surfaces, and particularly the inner portions of containers and the like. with an improved protective coating which will resist and impede the foregoing corrosive effects and maintain the tin surfaces in the desired form.

A yet further object of the present invention relates to the treatment of tin-plated surfaces in a novel manner by subjecting the said surfaces to a treatment which not only provides a. protective film but subjects the metal itself to a conversion adapted to render the surfaces insusceptible to etching, darkening or so-called weathering.

A yet additional objectof the present invention resides in the treatment or conversion of the outer surface portions only of tin containin materials such as, for example; tin-plate with a particularly a compound formed by oxidation or sulfidation,

Among other objects of the present invention are to provide an improved combination protective coating as above by direct action of suitable chemical compounds adaptedto produce the desired impervious and resistant coatings; and to apply'the treatment under predetermined conditions whereby to control the character of the protective films produced in respect to their corrosion-resistant properties as well as their appearance.

The present invention comprehends more particularly the treatment of tin surfaces by direct contact with the film-forming substances under conditions for promoting substantially immediate formation of the film and permitting these predetermined conditions to prevail for a predeter mined time to produce the desired degree and character of film formation.

The tin articles to be treated in accordance with the present invention include any articles or forms having exposed surfaces comprising tin, and in particular the present invention contemplates the treatment of containers formed of tinplate such as the conventional so-called tin cans and containers, particularly those of the type employed to store and contain foodstuffs. The tin-plate in general comprises a sheet of iron, steel or equivalent ferrous material having on its exterior surfaces a protective layer of tin which protects the iron or other material against con-o'- sion.

For treating the tin-containing surfaces and to produce an additional protective film thereon are preferably employed for direct treatments such chemical reagents or substances as are known oxidizing and/or sulfldizing agents with respect to tin and preferably such agents as may be employed to produce a relatively rapid film formation. That is to say, the function of the present reagents is to produce a. controlled and prompt film formation as oppo ed to any oxide formation which might or might not occur as the result of prolonged weathering or action of the atmosphere. Among the treating reagents which may be employed are preferably gases or vapors such as ozone, oxygen. preferably in concentrated form, or nitrogen oxide. So also, there may be employed strongly oxidizing vapors such as steam or hydrogen peroxide, and it will beunderstood that these reagents may be intermixed with each other in any desired proportion and also may be employed in admixture with air. So also, there may be employed, either singly or in admixture with the aforementioned ingredients, the gas hydrogen sulfide. The function of these reagents is to convert the exterior surfaces only of the tin in such a manner as to produce a protective film by chemical combination of the surf-ace tin with one or more of the elements in the aforementioned gases and vapors or by chemical combination of .the said surface tin with one or more elements of the air, the action being facilitated by the presence of the admixed substances. It will be understood that while many solid or liquid materials may lend themselves to this treatment, it is preferred, in accordance with the present in vention, to employ fluids of the type of gases or vapors which may be readily handled, particularly in conjunction with the treatment of preformed articles. 1

The treatment may be carried out at elevated or room temperature. Although the former is in general preferable in order to expedite the treatment, nevertheless in employing many rapidly acting agents satisfactory speed of reaction is obtained at ordinary temperature. In general, the temperature should not be above or substantially above the melting point of the tincontaining surfaces.

In carrying out the present invention the material may be treated either before or after it is shaped and placed in its final form. That is to say, in forming containers of tin-plate, for example, the provision of the chemical surface coating for the tin may occur while the tin is in its original sheet form, for example, since under the conditions prevailing in many known forming processes the chemical film is not harmfully affected. This, however, does not hold in the case of containers which are joined or sealed by the use of molten metal, such as solder, since it has been found that certain difiiculties may arise due to the fact that the fluid metal fails to wet the treated tin surfaces, particularly without the aid of special fluxes. For this reason accordingly, it may be found more desirable to treat the articles in their final form. In applying the present invention to the treatment of can containers, therefore, it is contemplated that the treating reagents be introduced into the containers after forming. According to one'preferred method of procedure, this treatment may be carried out in a conventional containeror can-filling machine, one or more of the desired treating reagents being introduced by means of the machine into the interior of the container. At the same time a heater may be provided for warming and'heating the container while it is being filled with the reagent fluid, or shortly thereafter, to the desired predetermined temperature. Operating a known machine of this character in this manner would obviously, therefore, result in the filling of the individual containers with the desired fluid or mixture of fluids and, where desired, subjecting the containers and their contents to an elevated temperature.

In carrying out the present invention accordmg to one exemplary method, a series of ordinary tents are permitted to escape. The articles so treated will be found, when cooled, to possess a satisfactory protective, dark colored coating on the interior surfaces capable of effecting resistance to etching and corrosion. In place of the above ingredients a mixture of hydrogen sulfide and steam may be applied to the containers.

According to another example, containers preformed of tin-plate are individually heated to a temperature of 350 to 400 degrees Fahrenheit and while so warmed are supplied with steam at 212 degrees Fahrenheit or above to which has been added an equal part of air which has been passed through an ozone machine to produce a substantial quantity of ozone therein. After one minute at this temperature the containers are cooled and vented to the air. 'A protective colored coating will be found to be formed on the interior surfaces of the container. It may be found desirable in some cases to subject the containers to treatment with steam at an elevated temperature for a period of as much as ten minutes to convert the tin surfaces to an advanced degree and to provide a deeper, brown tint or color thereon. It has been found desirable in practice to follow the above treatment by subjecting the containers to a blast of dry air injected through the ventholes for the purpose of sweeping out or displacing any moisture or moisture vapor which may tend to condense therein. The warm, dry air may be obviously passed through the ventholes by means of any conventional filling device as aforementioned. In place of the above mentioned reagent of ozone and steam there may be employed merely, steam or steam in admixture with air.

It will be understood that in place of preformed containers there may be employed any other type of plated articles, sheet material or other forms, and that the invention is not necessarily limited to the treatment of plated material but is similarly applicable to the treatment of any articles having surfaces comprising tin. i

It is important to point out that in accordance with the present invention there are employable in general all fluid substances which have relatively strong oxidizing or sulfidizing properties, that is to say, any gases or vapors which have the property of forming a uniform oxide or sulfide coating upon the surface of the tin-plate. It is of course undesirable to employ reagents which chemically interfere in any manner with the formation of such film or films or which tend to form other undesirable films. In general, it is preferred to provide a film of such character that it gives a glossy appearance of very faint amber or golden color. Such films have been found to strongly resist change and to protect the underlying surfaces in spite of long and indefinite periods of storage and contact with milk and other food products and particularly when applied to the interior surfaces of sealed containers.

Attention is directed to the fact that in the above illustrative examples employing air as a portion of the treatment mixture the product in each instance contains a normal content of moisture or humidity. It has been found in general that a certain percentage of moisture in any case facilitates the film formation action.

In place of the above sulfidizing agents there may be substituted various other equivalent substances of either organic or inorganic structure. Such, for example, are vapors of ammonium sulflde. methyl and ethyl sulfide, and the like.

as referring to the chemical mechanism of increasing the valence of other chemical elements.

Many variations of the above invention coming within the scope of the following claims will be evident to those skilled in the art in view of the above specification.

The invention is hereby claimed as follows:

1. A can or container of so-called tin-plate material for containing food products comprising bottom and side walls of sheet ferrous material having an integral, regular thin surface coating of tin,- the interior surfaces of said can being provided with an additional protective coating adapted to resist etching, discoloration and corrosionby the food products, said additional protective coating comprising a film of a sulfide of tin formed by subjecting said tin surfaces to agent.

, 3 chemical contact with a strong sulfidizing re- 2. A can or container of so-called tin-plate material for containing food products comprising bottom. and side walls of sheet ferrous material having an integral, regular thinsuriace coating of tin and having soldered joints, the interior surfaces of said can being provided with an additional protective coating adapted to resist etching, discoloration and corrosion by the food products, said additional protective coating comprising a film of sulfide of tin, said film being uniform and visible and being integrally associated 'with said tin surface.

3. A canor container of so-called tin-plate material, the interior surface of said can being uniformly coated with a thin film of tin sulphide.

4. A can or container having an interior surface formed of tin, said interior surface being uniformly coated with a protective film of tin sulphide. VICTOR NELSON. ALEX. C. HERRO. 

